In the manufacture of seamed, tubular sleeves of a heat shrinkable thermoplastic, such as a foamed polymer material, a web of such material is sized in width and cut repeatedly into discrete lengths or blanks. These blanks are picked up by a cylindrical mandrel and wound thereon such that the trailing edge overlaps the leading edge. As the edges overlap, a heat sealing device is pressed against the two-ply region of the wound blank to fusion weld or heat seal the two marginal edges together.
The sleeve formed by such procedure is axially transferred over a container, such as a glass bottle, and subjected to heat sufficient to shrink the sleeve in place in conforming relationship on the outer surface of the container. This form of glass container and printed shrunken sleeve cover is in popular use today.
The cycle just described is disclosed in U.S. Pat. No. 3,914,152 issued to S. A. Amberg, et al, wherein the heat sealing device includes an elongated sealing bar including an arcuate face or nose extending axially of the sleeve on the mandrel. The sealing bar is supported on a radius of the turret carrying the mandrel extending through the mandrel center axis. The mechanism supporting the sealing bar moves from a retracted position on a heater to the extended position whereat the bar face engages the overlapped plastic to apply heat and pressure, thereby sealing or seaming the axial extent of the portions of material in this overlap. The heat shrinkable polymeric material of the sleeve is sensitive to heat in that the heat sealing temperature of the seal bar should be maintained within limits; otherwise, the "seams" may be partially burned or otherwise improperly made such that in use the sleeve seams open up during or after shrinking the sleeve onto the container.